Surface protective films that are laminated on surfaces of metal plates, glass plates, synthetic resin plates, etc. to prevent surfaces of these articles from being damaged or to prevent dust, etc. from sticking to the surfaces are known.
As a surface protective film of this type, a surface protective film obtained by forming a pressure-sensitive adhesive layer composed of a composition containing a block copolymer and a tackifying resin, together with a polyolefin-based resin substrate through a co-extrusion method or the like is disclosed (see patent literatures 1 to 3).
With regard to this surface protective film, laminating by a co-extrusion method is possible, and a solventless pressure-sensitive adhesive can be attained, so that the film is excellent from the viewpoints of environmental protection and health safety during production. Further, since the production process can be simplified, the film is also economically excellent.
When a surface protective film is stored or conveyed as a wound roll that is obtained by winding the film into a roll, a pressure-sensitive adhesive layer wound on a back surface of a substrate is liable to strongly stick to the substrate.
As a result, feeding of the surface protective film from the wound roll is inhibited, and efficiency of an operation of bonding to the surface of an adherend is lowered. Further, if the surface protective film is forcibly fed, the substrate is partially extended and deformed, or the pressure-sensitive adhesive layer is partially delaminated, so that there is a fear that the film cannot be utilized as a surface protective film.
Thus, it is a problem to make stable adhesive strength of the surface protective film to an adherend and feedability thereof from a wound roll compatible with each other.
In order to solve the above problem, a technique of defining hardness of a pressure-sensitive adhesive to be within a specific range and thereby making stable adhesive strength to an adherend and feedability from a wound roll compatible with each other has been studied (see patent literatures 4 and 5).